Assembling the ductwork and exhaust on my Subaru 360

April 1, 2009:  What to do first?  At least I can assemble the exhaust and duct-work parts I have lying about.  I understand that the Subaru 360's engine performance is closely tied to the amount of "back-pressure", that is, the resistance the exhaust gasses meet when exiting the motor.  It needs a certain amount of back pressure - it presumably won't run as well if there was no prechamber and muffler bolted on.  SO THEN...

Having learned that the "correct" color for the inside of the engine bay is "body color", I scrubbed and painted the end of the bay where the parts would go.  I also wire-brushed and painted the bits involved - the pre-chamber, the air filter can, the two ends of the air intake duct.  I soaked all the rubber parts in armor-all for a day or two.

The upper part of the duct, in the "paint shop"
 The pre-chamber, ready to install

To help prevent an exhaust leak, I used "Permatex Red gasket maker" on both sides of the stock steel doughnut that will go between the pre-chamber with the muffler.  An off-label use, for sure.  It should be good to 650 degrees - we'll see if it helps here.
The duct-work, complete with cleaned up stock straps on the rubber,
and new foam insulation where the duct meets the body, in place

As the Subaru 360 has no exhaust valves that determine when the exhaust gasses are allowed to escape the cylinders, something else has to. 
Here is what the Subaru 360 Driver's Club "Book of Reprints" says about the exhaust system. 


If that's not enough, here's a detailed article on back pressure

And if THAT'S not enough, here is a cool animation that shows the effect of back pressure
(or the "rebounding shock wave") in the expansion chamber (pre-chamber). 
Note the green "good gas" trying to escape out the exhaust, and getting pushed back into the cylinder via back pressure...



Here is the engine bay with the muffler, pre-chamber and air filter can installed.  I will install the cowling after I am sure it's running well.



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